Method for filtering radon from a gas stream

ABSTRACT

The present invention relates to a method of filtering, at the end user&#39;s home, business or the like, a gas stream in which radon has been concentrated at sufficient levels to be a significant health hazard. Steps of the invention include: 
     (a) introducing the natural gas stream to a filter selected from a group that includes at least activated charcoal and impingement adsorbing media whereby radon concentrated in the gas stream at sufficient levels to be a health threat by a periodic loading of such network in which radon become clumped into packets due to dampening effects of the compressor-driven equipment and multiple customer outlet usage coupled with surprising long half life of the in situ radon, is filtered from the gas stream and captured irrespective of mode of transport, 
     (b) passing the filtered natural gas stream to the customer&#39;s gas appliance wherein safe use of the energy associated with the stream occurs, 
     (c) periodically and safely removing the filter of step (a) for disposing of captured radon, 
     (d) inserting a new filter in place of the removed filter of step (c).

SCOPE OF THE INVENTION

The present invention relates to a method of filtering. Moreparticularly, it relates to a filtering method to eliminate radon thathad been concentrated within a conventional gas line network atsufficient levels to be a health threat. As a further constraint, thesources of such radon concentration are identified. It is believed theyresult from a periodic loading of such network in which radon becomeclumped into packets due to, inter alia, electrostatic grouping,dampening effects of the compressor driven network and multiple customeroutlet usage that adds the aforementioned a periodic loading within thenetwork.

DEFINITIONS

In this application, "natural gas" means a mixture of gases associatedwith hydrocarbon accumulation within the earth as well as processed fuelgases derived from petroleum as well as mineral products susch as coalin either gas or liquid phases. In some gas line networks, the resultingfinal gases may be a mixture from these two sources but wherein theessential component consists of methane.

"Sufficient level to be a health threat" means a recognized standard forhuman health and safety established by authoritative bodies above whichcancer or reproductive toxicity in humans results, such bodies toinclude but not be limited to the U.S. Environmental Protection Agency(EPA), the U.S. Department of Food and Drug Administration (FDA) and theU.S. Department of Commerce. The EPA has set health and safety standardsfor radon which, if exceeded, would pose a risk to human health.

"Adsorption" means filter media that captures molecules of a gas, liquidor dissolved substance to the filter surface, by adhesion.

"Absorption" means filter media that absorbs molecules of a gas, liquidor dissolved substance to the filter itself, by taking in through poresor interstices.

"Impingement" means filter media that captures molecules of a gas,liquid, solid or a dissolved substance to the filter by physical capturesuch as by change in velocity.

"Radon" means radon gas and its components including both daughterisotopes thereof (although having the same atomic number, 222, isotopeshave different number of neutrons associated therewith), as well asdecay radionuclides thereof having relatively short lives but whichresulting decay chain, form parent elements such as lead and polonium.

BACKGROUND OF THE INVENTION

The danger of radon is well documented. Radon concentration levels at acustomer-end user's home, business and the like are not monitored,however. Believed to cause lung cancer, skin and organ damage, radonnaturally occurs in the earth during breakdown of radium, thorium andother radioactive elements, has a surprisingly high solubilitycoefficient in oil and natural or manufactured gases and hence is oftena component of natural gas. For example, local utilities have measuredup to 26 pico curies of radon on a radon test basis. Radon also is theheaviest of the family of elements called noble gases, is inert andbuilds a significant body burden as a function of frequency and level ofexposure due to its radioactivity and resulting decay chain components.While the EPA and various State Agencies may be aware of problem ofradon in gas lines, they do not think the exposure is of sufficientlevels requiring monitoring.

In such situation, I find that surprisingly large concentrations ofradon sporadically occur. Sources of such concentration: dampeningeffects of the compressor-driven network and multiple customer outletusage that add to a periodic loading of the natural gas stream coupledwith surprising longevity of the in situ radon. As a result, radon canflow to appliances in the custormer's home, business or the like atsufficient levels to be a health hazard, i.e., exceed Federal and/orState health and safety standards. Moreover, even though radon may becarried as a gaseous component of the natural gas or attach toparticulates and being inert, passes through the flame of the applianceunchanged (and hence exit from the appliance in original form), it hasbeen found that daughter isotopes also do not undergo change during suchcombustion. Yet still further, I have surprisingly found that the ironicelectrostatic charge of the latter is also altered as the host particleis destroyed. As a result, attachment of the exiting component canreadily reoccur adjacent to the appliance.

SUMMARY OF THE INVENTION

The present invention relates to a method of filtering, adjacent to theend user's home, business or the like such as the adjacent gasdistribution and processing system connected to the end user's meter, agas stream in which radon has been concentrated at sufficient levels tobe a significant health hazard. Steps of the invention include:

(a) introducing the natural gas stream to a filter selected from a groupthat includes at least activated charcoal and impingement adsorbing andabsorbing media whereby radon concentrated in gas stream at sufficientlevels to be a health threat by a periodic loading of such network inwhich radon become clumpled into packets due to dampening effects of thecompressor-driven equipment and multiple customer outlet usage that addto a periodic loading of the natural gas stream coupled with surprisinglongevity of the in situ radon, is filtered from the gas stream andcaptured,

(b) passing the filtered natural gas stream to the customer's gasappliance wherein safe use of the energy associated with the streamoccurs,

(c) periodically and safely removing the filter of step (a) fordisposing of the captured radon,

(d) inserting a new filter in place of the removed filter of step (c).

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a gas valve-meter assembly attached at oneend to a pipe of a gas line network adjacent to a home, business or thelike, along with a filtering assembly and by-pass network of the presentinvention;

FIG. 2 is a top view of the filtering assembly of the invention;

FIG. 3 is a section taken along lines 3--3 of FIG. 2;

FIG. 4 is an enlarged detail view taken along lines 4--4 of FIG. 3;

FIG. 5 is an enlarged detail of the filter media unit of FIG. 3;

FIG. 6 is an enlarged detail of an insert ring used in the filter mediaunit of FIG. 3; and

FIG. 7 is an alternate design for the filter unit of FIG. 5.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates a gas meter 10 connected via elbow 11 and gas pipe 12to a main gas line network (not shown). Downstream of the meter 10 is atee coupler 14 having a first end 15 connected to an overhead by-passnetwork generally indicated at 16, and a second end 17 connected througha first valve 18 and inlet fitting 19 to filter assembly 20. The filterassembly 20 in turn connects via outlet fitting 40, elbow 41 and asecond valve 42 to the overhead by-pass network 16. As shown, theby-pass network 16 includes a parallel by-pass valve 43. In operation,the by-pass valve 43 operates in complementary fashion with respect tofirst and second valves 18 and 42, respectively. When valve 43 isclosed, as shown, the valves 18 and 42 are open and the filter assembly20 is in operation. When valve 43 is open, the valves 18 and 42 areclosed and the filter assembly 20 is in a deactivated state.

FIGS. 2, 3 and 4 show the filter assembly 20 in more detail.

As shown, the filter assembly 20 includes a cap 21 fitted with arectangularly cross-sectioned dome 22 at its upper surface 21a, seeFIGS. 2 and 4, to which the pipe fittings 19 and 40 attach. The cap 21also has a lower surface 21b fitted with nipples 23 adjacent to a seriesof passageways that allow entry and egress of the gas stream: (i) inletpassageway 24 is L-shaped, is threadably connected to the inlet fitting19 at one end, and is also connected via central annulus 25 to interiorfilter media unit 26 concentric of vertical axis of symmetry 27; (ii) anoutlet passageway 28 that is bulbous over region 29 but is in fluidcontact with annular gathering region 30 that runs the full exterior ofthe filter media unit 26; the passageway is then swedged over region 31(in a L-shaped output form) at one end of bulbous region 29 forconnection to outlet fitting 40.

The cap 21 also has an annular side wall 21a, see FIG. 4, and inwardlyswedged at shoulder 32 and terminates at end 33. It is threadedtherebetween to engage with cylindrical canister 34. The canister 34includes a side wall 34a offset from the filter media unit 26 to formthe annular gathering region 30 previously described and in addition,has shoulders 35 and 36. The region between the shoulders 35, 36 and isthreaded to engage cap 21. Between shoulders 32 and 35 of the cap 21 andcanister 34, respectively, is grooved O-ring 37 to prevent gas leakageexterior of the filter assembly 20. The length of the engaging theadedportions of the cap 21 and canister 34 are constructed so that positivecontact exits only at the O-ring 37 and not at shoulders 33, 36.

Canister 34 also includes a bottom wall 34b. The bottom wall 34bincludes upwardly projecting nipples 38 concentric of a central annulus39. The latter attach to the filter housing 26. The purpose of thenipples 23 and central annulus 25 of the cap 21 as well as that of thenipples 38 and central annulus 39 of the canister 34 is to fixedlyreceive and hold the filter media unit 26 relative to the cap 21 andcanister 34.

Note that the direction of the gas stream at the interior of the filterassembly 20 is as taught by arrows 45, see FIG. 4. Such gas streamcannot pass directly from inlet passageway 24 to outlet passageway 28but is prevented to such flow due to the length of the annuli 25, 39.Thus the gas flow is in a radially expanding, sinusoidal pattern normalto the axis of symmetry 27 about horizontal axis A--A of the filtermedia unit 26. The pattern begins at the axis of symmetry 27 andprogresses through filter media unit 26, and ends exterior of the latterat annular gathering region 30. Thus the radon is filtered from thestream.

FIG. 5 illustrates filter media unit 26 in more detail. As shown, thefilter media unit 26 includes end pieces 50a, 50b each having a circularnotch 51 at outer surface 52 into which nipples 23, 38 of the cap 21 andcanister 34, respectively, are received. Such construction permits theend pieces 50a, 50b to take up firm surface contact with the cap 21 andthe canister 34 as the cap 21 is threaded to the latter.

Interior of the end pieces 50a, 50b are a series of concentric tubes 53,54, 55, 56 and 57 fitted into the notches 51 of the former. The tubes53-57 have side wall fitted with perforations 59. The side walls arenormal to the horizontal axis of symmetry A--A previously mentioned, thelatter being also normal to the vertical axis of symmetry 27. Theperforations 59 permit gas flow in the sinusoidal-like, single passfiltering manner relative to axis A--A within the tubes 53-57 asindicated by arrows 45. As shown these arrows 45 begin near the verticalaxis of symmetry 27 and serpentine outwardly in sinusoidal fashionthrough the filter media unit 26.

Note that between the tubes 53 and 54; between tubes 54 and 55; betweentubes 55 and 56 and between tubes 56 and 57 are separate filter medium60, 61, 62 and 63 together forming a four-stage, single pass filteringmedia which in combination remove all radon from the gas stream. Themedia 60-63 are each selected to remove radon from the gas stream inprogressive fashion, viz., from microscopic to millimicrospic levels viasingle passage of the gas stream through each medium 60-63. However, themedia 60-63 do not filter the methane from the gas stream.

FILTER MEDIUM 60

In this regard, filter medium 60 is preferably pleated filter paperhaving the following characteristics. Pleated filter paper 60 is widelyavailable, performs impingement, absorption and adsorption and is madeby conventional manufacturing processes including but not limited tomethods involving weaving of cellulose, wool, acrylic, rayon fibers intocorrugated sheet form. The tips and troughs of the corrugated pleatedfilter paper 60 of FIG. 5 are located in accordion fashion across andwithin the tubes 53, 54 but not in contact with the upper and lower endpieces 50a, 50b of the filter media unit. As shown in FIGS. 5 and 6, aseparate ring 64 is fitted in contact with each end piece 50a, 50b. Thering 64 of rectangular cross section, includes side wall 66 andterminating broad surface 67, that is compressively fitted in snugcontact with the upper or lower end piece 50a, 50b. As a result, the gasstream can circulate in the manner shown and pass through the pleatedfilter paper 60 in single pass fashion between inlet and outletperforations 59 associated therewith.

The density of paper 60 varies to provide filtering of radon that may becarried on dust, rust, dirt, moisture and oil laden particles in a rangeof 40 to 750 microns. It also retains both oils and moisture.

FILTER MEDIUM 61

In this regard, filter medium 61 is preferably silica gel in crystallineform located between tubes 54 and 55.

Silica gel 61 is a conventional drying and dehumidifying agent formed ofamorphous silica in crystalline form for filtering and trapping radontransported by water in gaseous form as well as smaller diameter dirtand dust particles carrying radon piggyback. The gel absorbs moisturewithin the gas stream but not oils and is located between tubes 54 and55. The medium 61 provides for single passage filtering operations only.

Calculations associated with the above are as follows:

Average Natural Gas Usage

Assume average gas use is 125 MSCF/YR, then per month usage cubic metersis

    125 mcf/yr/12=10,416.6 cu. ft/month/35.3=295 cu. meters/month

Assume the area between tubes 54, 55 is a function of a mean diameter of35/8 inches, a height of 5 inches and thickness of 0.875 inches, then

Filter volume=52.5 cu. inches.

FILTER MEDIUM 62

Filter medium 62 is preferably open pore polyurethane foam for capturingradon in gaseous form. Filter medium 62 filters by impingement andadsorption and retains micro vapors and solid particulates includingoils and is located between tubes 55 and 56 for single pass filteringoperations. It has the following characteristics.

Shape: Cylindrical shape from sheet form

Cellular Matrix Structure

Medium density--0.1 to 0.4 g/cu. cm matrix solid foam to gas insert

Porosity--0.14 to 0.41 (i.e. 70% to 90% open pore polyurethane)

Sample Period--2 months AT 100% Retention Well below breakthroughvolume, viz., the point at which concentration of solute in the columneffluent is half the concentration introduced into the column.

Volatility--Medium, See below

Preparation--Cut from foam sheets; air dry; install.

Pressure Drop--0.015 psi Calculations associated with the above are asfollows:

Assume average gas use is 125 MSCF/YR, then per month usage cubic metersis

    125 mcf/yr/12=10,416.6 cu. ft/month/35.3=295 cu. meters/month

Filter volume=408.28 cu. cm via 5 inches height by 1/2 inches thicknessby 15.7 inches long;

Efficiency--700 cu. meters available

Change frequency=700/295=2.38 months

FILTER MEDIUM 63

Futhermore, filter medium 63 is preferably granular activated charcoallocated between tubes 56 and 57 for single pass filtering operations.

Granular activated charcoal is a conventional filtering medium, performsfiltering on liquids, gases and solid particulates down to 10 Angstromsin size (but does not retain water) by impingement and adsorption and isprepared by carbonization of raw materials such as wood, coconut shelland coal. It attracts and holds radon irrespective of the mode oftransport such as a gas alone or piggyback aboard dirt and dustparticles as well as with liquid plugs.

Physical properties:

Surface Area=600 to 1050 cubic meters per gm

Density=0.92 to 2.0 grams per cubic meter

Effective size=0.8 to 1.5 mm

Pore volume=0.6 to 1.7 cubic per cm gram

Mean diameter=1.2 to 1.7 mm

Sieve Size=No. 8 to No. 40 (U.S. Series)

Iodine No.=650 to 1,000

Calculations associated with the above are as follows:

Assume average gas use is 125 MSCF/YR, then per month usage cubic metersis

    125 mcf/yr12=10,416.6 cu. ft/month/35.3=295 cu. meters/month

Assume the area between tubes 54, 55 is a function of a diameter of 7inches, a height of 5 inches and a thickness of 0.5 inches, then

Filter volume=55. cu. inches;

Filter volume available=1400 cu meters

Change frequency=1400/295=4.6 months

FIG. 7 illustrates an alternate filter media unit 69 in more detail.

As shown, the filter media unit 69 is similar to the filter media unit26 previously described, such filter media unit 69 having end pieces 70,71 fitted with inwardly facing notches 72 (relative to a horizontal axisof symmetry, not shown), and a series of concentric tubes 73, 74, 75, 76and 77 collinear with axis of symmetry 78. However, perforations 79 areprovided in side walls of tubes 73-77 to allow radial flow outwardlyfrom vertical axis of symmetry 78. Such construction does not permit thesinusoidal flow as previously mentioned, however. Instead, a gas streamflows as an annular mass through the filter media unit 69 beginning atthe axis of symmetry 78 and ending at the exterior of tube 77. Suchpattern is indicated by arrows S that are seen to expand outwardly fromthe axis of symmetry 78. The notches 72 aid in assembly as they take upfirm surface contact with the cap 21 and canister 34 of FIGS. 2, 3 and4, as the former and latter are threaded together.

Between the tubes 73 and 74; between tubes 74 and 75; between tubes 75and 76, and between tubes 76 and 77 are separate filter medium 80, 81,82 and 83 together forming a four-stage filtering media which incombination remove radon from the gas stream. That is, the media 80, 81,82 and 83 are selected to remove all traces of radon from the gas streamin the same order and similar filtering capacity as previously discussedwith reference to FIG. 5. In this regard, filter medium 80 is pleatedpaper, medium 81 is silica gel, medium 82 is open pore polyurethane foamand medium 83 is granular activated charcoal each having characteristicsas set forth above.

GUIDELINES FOR SELECTION OF FILTER MEDIA 60-63 AND 80-83

Radon exists in a single state within the gas line network: as a vapor.It is carried along because of the pulsation of the gas stream andsurprisingly because of the gas phase transition effects created by thedrive compressors of the gas system augmented by the multiple outletdemands of the customers. Hence no matter how the radon is carried inthe gas stream, the former are trapped within the filter media 60-63 and80-83 of the invention.

Gas phase transition is a little understood phenomenon in which variousdynamics due to changes in temperature, pressure, pipe size, flow ratesthat cause interaction between hazardous elements of the gas stream andvarious other elements in the network, such as pipe coatings, plug flows(aggregations of materials moving as a group) liquids and gaseous phasesof the natural gas stream. As a result, liquids and gases within thenatural gas stream surprisingly change state. The resulting gaseousphase may contain the hazardous elements which are transported greatdistances.

As a vapor, the radon is then carried along under like sets ofcircumstances described above.

PRESSURE CONDITIONS

As surface residue on solid particulates, radon is carried along asfollows. At the well site, pressures in access of 2,000 psi occur. Suchpressure can be maintained until stepped down to about 1,000 psi, thenceto 60 psi and finally to about 1/2 psi at the user's residence orbusiness.

While filter media 60-63 and 80-83 are preferably as discussed above,substitutions can be made. For example, other types ofimpingement-adsorbing media could be used including silica sand,activated clay such as montomorillanite, natural zeolites composed ofhydrous calcium and aluminum silaceous materials, synthetic zeolitescalled molecular sieves such as sodium aluminum silicates, caitlin siltloam, dried corn husks, etc. Also, fluid baths, sonic collectors,electrostatic precipitators and thermal de-humidification devices couldalso be used.

Other impingement adsorbing media includes other packings such as can bewoven, coated or impregnated (such as with glycerol, glycerin, oils,glycol etc.). Other types of filters include membrane filter media foruse in natural gas environments generally above 100 psi in which thesolute is the force that helps perform the filtering, as well as specialfilters such as elongated, inter-latticed baffles that provideelectrostatic collection such as the HEPA filter (High EfficiencyParticle Accumulator filter, an acronym of The National Aeronautics andSpace Administration).

In some applications, fluid baths could be used, in which fluidsselected from a group that includes water, oil, alcohol, glycerol,glycerin, and glycol, could be used. Such use would require amodification to the canister 34 in order to provide a filteringoperation.

FURTHER METHOD ASPECTS

After installation has occurred, the filter system is an activefiltering state for radon. That is to say, the valve 43 in the by-passnetwork 16 is closed and the valves 18 and 42 upstream and downstream ofthe filtering assembly 20 are opened.

When the filtering assembly 20 is to be re-charged, the valve 43 in theby-pass network 16 is opened so that gas is passing in parallel to thedownstream appliances (not shown). This assures ample gas supply beforethe filtering assembly 20 is deactivated. Such deactivation occurs whenthe valves 18 and 42 are closed. Then the canister 34 with the filtermedia 60-63 and 80-83 captured within its side wall 31, is removed fromcontact with cap 21, and the canister 34 and filter media 60-63 and80-83 are removed for transport to a waste station and disposal. A newcanister 34 with new filter media 60-63 or 80-83 is then re-attached tothe cap 21.

The above description contains several specific embodiments of theinvention. It is not intended that such be construed as limitations onthe scope of the invention, but merely as examples of preferredembodiments. Persons skilled in the art can envision other obviouspossible variations within the scope of the description. For example,the filter assembly 20 can be inserted in higher pressure lines of thegas transfer network, such as within the local utilities' pipingnetwork. Hence the scope of the invention is to be determined by theappended claims and their legal equivalents.

What is claimed is:
 1. A method of filtering, adjacent to an enduser-customer's residence or business in which at least a single gasappliance is located, a natural gas stream in which radon has beenconcentrated at sufficient levels to be a health threat in a natural gasgathering and distributing network, comprising the steps of:(a)introducing the natural gas stream to a filter selected from a groupthat includes impingement, absorbing and adsorbing media whereby radonconcentrated in the gas stream at sufficient levels to be a healththreat by aperiodic loading of the natural gas within the gathering anddistributing network, are filtered from the gas stream and capturedirrespective of mode of transport, (b) passing the filtered natural gasstream to the customer's gas appliance wherein safe use of the energyassociated with the stream occurs, (c) periodically and safely removingthe filter of step (a) for disposing of captured radon, (d) inserting anew filter in place of the removed filter of step (c).
 2. The method ofclaim 1 in which said impingement, absorbing and adsorbing media of step(a) for filtering radon, are selected from the group comprising pleatedfilter paper, silica gel, open pore polyurethane foam and granularactivated charcoal.
 3. The method of claim 2 in which said impingement,absorbing and adsorbing media of step (a) comprises in seriatim, pleatedfilter paper, silica gel, open pore polyurethane foam and granularactivated charcoal whereby radon is removed from the natural gas stream.4. The method of claim 1 in which step (a) is further characterized byaperiodic loading of in situ radon being the result of gas phasetransition effects occurring within the natural gas gathering anddistribution network.
 5. The method of claim 4 in which step (a) isfurther characterized by the natural gas gathering and distributingnetwork including compressor-driven equipment and multiple customeroutlets connected to such equipment and by aperiodic loading of in situradon within the natural gas gathering and distributing network beingthe result of dampening effects of the compressor-driven equipment andmultiple customer outlet usage.
 6. The method of claim 5 in which thenatural gas gathering and distributing network includes gas meters eachconnected to one of the outlets of the network and wherein saidfiltering occurs after such gas stream exits from the end user's gasmeter.
 7. The method of claim 1 in which said filtering occurs in thenatural gas gathering and distributing network.
 8. A method of filteringadjacent to an end-user-customer's residence or business in which atleast a single gas appliance is located, a natural gas stream in whichradon has been concentrated at sufficient levels to be a health threatwithin a natural gas gathering and distributing network connected to thecustomer's gas appliance comprising the steps of:(a) introducing thenatural gas stream to a filter selected from a group that includesimpingement, absorbing and adsorbing media whereby radon concentrated inthe gas stream at sufficient levels to be a health threat due toaperiodic loading within the natural gas gathering and distributingnetwork, is filtered from the gas stream and captured irrespective ofmode of transport, (b) passing the filtered natural gas stream to thecustomer's gas appliance wherein safe use of the energy associated withthe stream occurs.
 9. The method of claim 8 with the additional stepsof:(c) periodically and safely removing the filter of step (a) fordisposing of captured radon, (d) inserting a new filter in place of theremoved filter of step (c).
 10. The method of claim 8 in which saidimpingement, absorbing and adsorbing media of step (a) for filteringradon is selected from the group comprising pleated filter paper, silicagel, open pore polyurethane foam and granular activated charcoal. 11.The method of claim 10 in which said impingement, absorbing andadsorbing media of step (a) comprises in seriatim, pleated filter paper,silica gel, open pore polyurethane foam and granular activated charcoalwhereby radon is removed from the natural gas stream irrespective ofmode of transport.
 12. The method of claim 8 in which step (a) isfurther characterized by aperiodic loading of in situ radon being theresult of gas phase transitional effects occuring within the natural gasgathering and distributing network.
 13. A method of claim 12 in whichstep (a) is further characterized by the natural gas gathering anddistributing network including compressor-driven equipment and multiplecustomer outlets operationally connected to such equipment and whereinstep (a) is also characterized by clumping of in situ radon that is theresult of dampening effects produced by the compressor-driven equipmentand multiple customer outlet usage within the natural gas gathering anddistributing network.
 14. The method of claim 13 in which the naturalgas gathering and distributing network includes gas meters eachconnected to one of the outlets of the network and wherein steps (a),(c) and (d) occur after the natural gas stream exits from the end user'sgas meter.
 15. The method of claim 13 in which steps (a), (c) and (d)occur within the natural gas gathering and distribution network.